HiI need to make a more than 70 years countdown in seconds, i could turn off and turn on without loosing count. ( then i'd like to link it with sensors )The main question is : Can arduino uno handle this ?

For now i have 10 seven segments common cathode displays / 2 Max7219 chips, and i roughly understood why i should use these to link the displays and have a clean signal but i'm still far away from being able to do it by myself.

Put a battery backed RTC on it, can check the displayed time left against the actual current time & adjust accordingly.Then all you need to store is the end date. Replace the battery every few years.70 years * 365.25 days/year * 24 hr/day * 60 minutes/hr * 60 seconds/hr = 2,209,032,000 secondsGuess that is 10 digits.

Thank you very much for your answers.First excuse me, I was not very clear. The idea is to have it running for a little more than 70 years, but when it's off i just want it to remember when it stops and start at the last knew count when i turn it back on. So is real time clock necessary ? i guess i'll need a independent battery device anyway.

The next steps are :

1- getting the 10 diplays, the 2 max7219, the memory device, and the arduino mounted correctly together. I'll try to do it by myself but if you can give me any advice or link or help, it will be welcome.

2- put the right countdown program in the arduino.

3- link the two sensors that can pause the countdown when they are both activated.

I'll share my progessions with youIf i make any mistake in my steps feel free to warn me, i only wish to learn.

You might invest some time in sleep modes of the Arduino as only once per second the clock needs to be adjusted. The rest of the time it can sleep. So your battery will last longer (you might use some super capacitor)